Inkjet printing is a method for producing images by the selective deposition of ink droplets on a print medium, such as paper, film, fabric and other substrates. Digital data is provided to the print engine to drive the selective deposition of the ink droplets in a pattern that forms the desired image. Inkjet printing can be in color or monochromatic. Because of their many advantages, inkjet printers have found broad applications in such diverse fields as industrial labeling, short run printing, desktop publishing and pictorial printing.
The inks used in various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is molecularly dispersed or dissolved in a carrier medium such that discrete colorant particles cannot be observed. The carrier medium can be a liquid or a solid at room temperature. In pigment-based inks, the colorant exists as discrete particles suspended in a carrier medium. These pigment particles are usually treated with dispersants or stabilizers which keep the pigment particles from agglomerating and/or settling out of suspension.
Ideally, the ink used in an inkjet printing system should meet various performance parameters. These parameters may include certain physical properties of the ink such as viscosity, surface tension, and electric conductivity that work well with the discharging conditions of the inkjet print head, such as the driving voltage and driving frequency of the ink discharge means in the print head, the form and material of print head discharge orifices, the diameter of the orifices, etc. The ink should also be able to remain in storage for prolonged periods of time without causing subsequently clogging or other complications in the print head. The ink should not chemically attack, corrode or erode surrounding materials such as the ink storage container, print head components, etc. The ink should be non-toxic, flame-resistant and without any unpleasant odor. The ink should also exhibit low foaming and high pH stability characteristics.
The ink should be quickly fixable onto a print medium such that an image formed appears smooth without revealing the individual drops of ink used to form the image. Once formed into the desired image on the print medium, the ink should have strong water resistance and light resistance, meaning that the image will resist being degraded by exposure to either moisture or strong light. The ink of the printed image should also have high adhesion to the print medium and be resistant mechanical damage such as scratching.
In order to promote these desirable characteristics of an inkjet ink, specifically, a pigment-based ink, it has been suggested to encapsulate the colorant particles in a pigment-based ink. However, previous attempts to encapsulate colorant particles in a pigment-based inkjet ink so as to promote desired ink characteristics without otherwise degrading the ink's performance have met with very limited success.